What is overweight and obesity?

At their most basic, the words “overweight” and “obesity” are ways to describe having too much body fat.

The most commonly used measure of weight status today is the body mass index, or BMI.

BMI uses a simple calculation based on the ratio of someone’s height and weight (BMI = kg/m2). Decades of research have shown that BMI provides a good estimate of “fatness” and also correlates well with important health outcomes like heart disease, diabetes, cancer, and overall mortality.

Healthy BMI Ranges for Adults and Children

What’s considered a healthy BMI?

For adult men and women, a BMI between 18.5 and 24.9 is considered healthy.
Overweight is defined as a BMI between 25.0 and 29.9; and a BMI of 30 or higher is considered obese.

As in adults, obesity is also a growing problem in children and adolescents. Because children grow at different rates, depending on their age and gender, the definitions of overweight and obesity in children and adolescents differ from those in adults.

In the U.S., for example, the definition is based on standard growth charts developed by the Centers for Disease Control and Prevention. In children and adolescents age 2 to 20 years old, a BMI in the 85th to 94th percentiles for age and gender is considered overweight; a BMI in the 95th percentile or higher is considered obese.

Waist Size Matters: Abdominal Obesity

One important category of obesity not captured by BMI is so-called “abdominal obesity”-the extra fat found around the middle that is an important factor in health, even independent of BMI.

The simplest and most often used measure of abdominal obesity is waist size. Guidelines generally define abdominal obesity in women as a waist size 35 inches or higher, and in men as a waist size of 40 inches or higher.

Measuring Body Fat

There are a number of ways to measure body fat. Some are well suited to the doctor’s office, such as calculating a person’s BMI. Other, more complex methods require specialized equipment, such as magnetic resonance imaging or dual energy X-ray absorptiometry machines; while these machines can measure body fat very accurately, they are typically only used for this purpose in research settings.

Globally, there are 1.5 billion adults who are either overweight or obese, a number expected to increase to 3 billion by 2030. The epidemic is reaching catastrophic proportions, and one of the key-if small- steps to bringing it under control is to have a common language to describe the problem.

Key facts

Obesity is defined as excessive body fat that increases your risk of other health problems.
A person with a body mass index (BMI) above 30 is considered obese, while a person with a BMI between 25 and 30 is considered overweight.
Most people become obese or overweight because they take in more energy from food and drink than they use with physical activity.
In most cases, a kilojoule-controlled diet with regular exercise will help you lose weight and feel healthier.

Being obese or overweight means you are carrying too much weight and body fat. Being obese puts you in the highest weight range, over what’s considered healthy. Being overweight also means your body weight is outside a healthy range, but it’s not as extreme as obesity.

In Australia, 2 out of 3 adults, and 1 in 4 children are obese or overweight. Obesity is also more common among disadvantaged Australians. Experts predict that by 2025, more than three-quarters of Australian adults will be either obese or overweight.

Obesity can be a sensitive topic. Obesity is not just about appearance, since it increases a person’s risk of heart disease, type 2 diabetes and other serious conditions. Adopting healthy eating habits and regular exercise can help you manage obesity. In some cases, your doctor might also recommend medicines or surgery to help with weight loss.

What are the signs of obesity?

The most visible sign of obesity is excess body fat, usually measured by BMI. A BMI of 30 or more indicates obesity, while a person with a BMI between 25 and 30 is considered overweight.

You can calculate your BMI using Healthdirect’s calculator for adults. However standard BMI calculations can inaccurately measure a healthy weight for people under 18 years of age, pregnant women, and people from certain ethnic backgrounds. If you’re usure, ask your doctor or dietitian if BMI applies to you.

NEED TO LOSE WEIGHT? — Use the BMI Calculator to find out if your weight and waist size are in a healthy range.

What causes obesity?

For most people, obesity happens gradually by taking in more energy than your body needs over time. Food and drinks contain energy (measured in kilojoules), which your body burns, especially during physical activity. The average adult needs 8700kJ each day, and any extra energy you consume is stored as body fat. That’s why, over time, over-consuming food and drink without also increasing activity leads to weight gain.

Controllable factors

Obesity develops gradually from poor diet and lifestyle choices, such as:

eating junk food frequently — fast food meals, cakes and pastries, sweets, processed meats and sugary drinks are loaded with kilojules.
drinking too much alcohol , which contains a lot of kilojoules with no nutritional benefits.
avoiding physical activity — only half of Australians do enough physical activity for good health.

There isn’t usually a single answer behind why someone chooses to eat or drink too much. Stress, low mood, lack of motivation, changing emotions or poor access to healthy options can all cause people to consume more kilojoules than they need.

Other causes

Obesity can also result from other factors, such as:

your family history — the habits you grew up with and the genes you inherited from your parents.
your surroundings — what kinds of food are available and in what portions, where you work and sleep.
your metabolism — how efficiently your body turns food into energy.
certain medical conditions that cause weight gain, such as hypothyroidism.
certain medications can cause weight gain as a side effect, such as antipsychotic medications.

Whatever the cause of your obesity, your doctor can help you address your weight and improve your health.

When should I see my doctor?

See your doctor if you are overweight or obese and want to lose weight.

You can discuss things including:

assessing your BMI, waist measurement and health risks regularly,
how to improve your diet,
how much and what type of exercise is appropriate for you, and
whether you need further tests or treatments for obesity-related conditions.

FIND A HEALTH SERVICE — The Service Finder can help you find doctors, pharmacies, hospitals and other health services.

How is obesity diagnosed?

Body mass index

Your doctor will measure your height and weight to calculate your BMI, and to assess whether you are obese or overweight.

For most adults:

a BMI between 18.5 and 24.9 is considered healthy
a BMI between 25 and 29.9 is considered overweight
a BMI of 30 and above is considered obese

A BMI measurement may be less accurate in certain groups of people who naturally have different proportions in muscle and fat mass. For example, athletes with high muscle mass may weigh in as obese based on the BMI, when they are actually a healthy weight.

Waist circumference

Your doctor may also measure your waist circumference to assess your weight. Obesity-related health problems such as type-2 diabetes, heart disease and some cancers are more likely if you have a waist circumference of 94cm or more (for men) or 80cm or more (for women who aren’t pregnant).

Other tests

Your doctor may also measure your blood pressure, blood glucose (sugar) and lipid (cholesterol) levels to assess your risk of other conditions associated with obesity.

How is obesity managed?

Unfortunately, there is no ‘quick fix’ treatment for obesity. In most cases, a kilojoule-controlled diet with regular exercise will help you lose weight and feel better. It’s also important to stay positive.

Reducing your kilojoule intake

One way to lose weight is to change your diet to create an energy deficit. You can do this by swapping unhealthy and high-energy food choices such as fast food, processed food, sugary drinks and alcohol, for healthier choices such as vegetables and fruit. Be careful of diets that encourage unhealthy behaviours or restrict certain foods completely. When planning to change your diet, it may be helpful to speak with a dietitian about a tailored food program.

Increasing physical activity

To lose weight, it’s also important to combine diet changes with at least 30 minutes of moderate-intensity physical activity each day — anything that requires more effort than usual, such as brisk walking, swimming or playing tennis.

Many physical activities can fit into your daily life, such as taking the stairs instead of the lift, physically playing with your children, taking public transport or cycling. You may find it helpful to join an exercise group or sports team for motivation and support.

Research shows that:

doing any physical activity is better than doing none;
incorporating daily physical activity is more effective than only once or twice a week
strength or resistance training exercise (exercising with weights) at least twice a week is particularly helpful for your metabolism (how fast you burn energy) and bone health.

Supporting your weight loss

If you’ve found it hard to lose weight in the past, it may be helpful to see a counsellor or psychologist who can help you with long-term changes. Techniques such as cognitive-behavioural therapy can help make it easier to lose weight by teaching you to recognise when and why you eat, or to change unhelpful thoughts or thinking patterns. Your doctor can refer you to a counsellor or psychologist.

Weight-loss medicines

Prescription medicines are available for weight loss in Australia. However, it's important to use these in combination with reducing your kilojoule intake and increasing physical activity. Some medicines work by reducing the amount of fat you absorb from food, while others make you feel less hungry. Weight loss medicines have side effects and aren't suitable for everyone. Talk to your doctor or pharmacist before starting a weight-loss medicine to see if it's right for you.

Weight-loss surgery

Bariatric surgery can help some people lose weight by changing the way the body digests and absorbs food. When considering weight loss surgery, your doctor will take into account aspects such as your BMI, whether you’ve tried other methods to lose weight, and how much obesity affects your daily activities.

Complementary therapies and supplements

There are many alternative treatments and pills that are said to work wonders for obesity and weight loss. But they shouldn’t replace the proven methods, described above.

Are there complications of obesity?

Being obese or overweight is associated with several other conditions. These include:

You doctor can assess whether you’re more likely to experience health complications because of your obesity.

ARE YOU AT RISK? — Are you at risk of type 2 diabetes, heart disease or kidney disease? Use the Risk Checker to find out.

Resources and support

For more information and support, try these resources:

Call GetHealthy NSW on 1300 806 258 for free phone-based health coaching to help you reach your own healthy lifestyle goals.
The Dietitians Association of Australia has nutrition information, tips and recipes to help you eat well
LiveLighter offers a range of tools and calculators to help you make lifestyle changes to improve your health.